Fluid flowmeter



March 26, 1968 E. H. SCHWARTZMAN 3,374,674

FLUID FLOWMETER Filed Feb. 25, 1965 6 Sheets-Sheet 2 CO/L C /25 //a //6A22 N6 4% J ATTORNEYS March 26, 1968 E. H. SCHWARTZMAN 3,374,674

FLUID FLOWMETER Filed Feb. 23, 1965 6 Sheets-Sheet 5 INVENTOR 51 452577SCHH AETZMA/V ATTOE/VEYS Mam}! 1968 E. H. SCHWARTZMAN 3,374,674

FLUID FLOWMETER Filed Feb. 25, 1965 6 Sheets-Sheet 4 INVENTOR. EVE/86773SC /114487244 BY WL/xm, 4 2&0! 5

E. H. SCHWARTZMAN March 26, 1968 FLUID FLOWMETER .D +u e e h w s t e e hS 6 J I Filed Feb. 23, 1965 p/V/FEQ INVENTOR. EVER/577A SCHWAQTZ/lM/VMarch 1968 E. H. SCHWARTZMAN 3, 74,67

FLUID FLOWMETER Filed Feb. 23, 1965 6 Sheets-Sheet 6 INVENTOR. fVf/QETI'HSKHWAQTZMA/V ATTO/QA/EVS United States Patent Ofilice 3,374,674Patented Mar. 26, 1968 3,374,674 FLUID FLOWMETER Everett H. Schwartzman,457 34th St., Manhattan Beach, Calif. 90266 Filed Feb. 23, 1965, Ser.No. 434,179 14 Claims. (Cl. 73213) ABSTRACT OF THE DISCLOSURE Aflowmeter including two generally-similar, venturi members definingtapered internal passages, which members are held independently spacedapart by diaphragm structures so as to receive the fluid stream that isto be measured. The spaced displacement of the venturi members allowsthem to respond to variations in fluid flow with opposed movements whichare sensed by electrical apparatus to manifest the measured flow as anelectrical signal. The requisite opposed movements of the venturimembers to measure flow renders the structure immune from various otherfactors, as acceleration forces and so on. The disclosure includesinductive, capacitive and resistance elements for providing anelectrical signal indicative of flow.

This invention relates generally to measurement of the flow or" fluids,gaseous or liquid, along a given path or direction; and moreparticularly the invention relates to a system and method which utilizenovel concepts in electromagnetic electromechanical transducers andsensors.

In contemporary industry and modern research and develop-ment endeavorsthere has arisen a heretofore unfulfilled need for a flowmeter foraccurately measuring the flow of fluid substances such as liquid oxygenat high pressures and at extremes of velocity and temperature.

Transducers heretofore available have provided measurements which aresubject to errors due to non-constant characteristics of the fluid suchas its viscosity, density, thermo-conductivity or the like. In addition,the instruments are typically mechanically unstable, fragile, or bulkyor are costly and require complex electrical circuitry to compensate fortheir inherent nonlinearity. Furthermore, the prior art transducers aregenerally incapable of insertion into a chemically active (e.g., acid)flow. In addition, they are typically gravity sensitive, requiring thatthey be placed and maintained in a particular orientation with respectto the direction of the field of gravity and are acceleration sensitivecausing their electrical output to be spurious whenever the transduceris subjected to mechanical shock or other acceleration of the unit orits component parts.

Other disadvantages and limitations of prior art devices include theirslow response time which precludes or limits their use in recordingtransients and in many other applications. Similarly, their utilizationof a particular transducer is limited to a relatively narrow. range offlow velocities. Some prior art systems depend upon a rotating propelleror other similar device mounted on a shaft in the path of the fluidflow. The rotational velocity of the propeller, driven by kinematics ofthe fluid flow, is then coupled out of the fluid conduit or otherenvironment of the flow and converted into a signal representative ofthe velocity of the fluid. Such transducers suffer many of thedisadvantages pointed out above and in ad dition introduce severelubrication problems for the bearing of the rotating device,particularly in a cryogenic, radioactive, or chemically activeenvironment. Furthermore, any mechanical connection between the rotarydevice and external components also presents serious problems of bearinglubrication and leakage. Any leakage is of course absolutely intolerablein many modern fluid flow applications. 1

It is, therefore, an object of the present invention to provide aflowmeter system and method which are not subject to these and otherdisadvantages of the prior art.

It is another object to provide such apparatus including a transducer orelectrical sensing component which may provide, when desired, anelectrical effect which is directly proportional to the velocity of thefluid flow.

It is another object to provide such a system which is extremelyaccurate and sensitive and which is not subject to errors due to changesin density, viscosity, temperature or other characteristics of thefluid.

It is another object to provide such apparatus which is mechanicallyrugged, stable and compact, relatively inexpensive, and which does notrequire bearing surfaces within the fluid or mechanical couplings,bearings, or packing boxes through the fluid containing walls and whichis fully operable in environments of temperature and pressure extremesand radioactivity.

It is another object to provide such apparatus which has a response timeof an order of a fraction of a millisecond and which is neitherorientation nor acceleration sensitive.

It is another object to provide such a system which does not cause anappreciable pressure drop in the fluid flow being observed.

Briefly, these and other objects of the invention are achieved in oneexample of the invention which includes a pair of closely spaced,axially aligned, hollow cylindrical armature members which areinternally tapered whereby their contiguous ends have a smallerdiameter, in this example, than their opposite ends. The armaturemembers may be metal and are supported at each of their ends by annular,flexible metal diaphragms. The inregister bores of the diaphragms andarmature members define the path of the fluid flow through the sensor;and the combined tapered bores form a venturi having a reduced diameterregion near the axial mid-point of the combined armature members. Thereduced diameter portion is coupled to the annular volume between thetwo juxtaposed center diaphragms while fluid pressures in the enlargeddiameter end portions of the venturi are coupled to the outer surface ofeach of the outer supporting diaphragms. Thusly, when the fluids arepassed through the combined tapered bores of the sensor, the pressureand consequent outward axial forces on the central diaphragms are lessthan that exerted axially inwardly on the outer diaphragms by a netforce which depends on the velocity of the fluid. Consequently, thearmature members are displaced axially toward each other against theretaining, restoring forces of their supporting diaphragms, by adisplacement, the magnitude of which is the measure of the velocity ofthe fluid flow.

Each of the armature members may carry a paramagnetic ring or ferrulewhich constitutes an element of a. magnetic circuit separated from otherlower reluctance elements thereof by an air gap, the instantaneousreluctance or gap dimension of which is determined by the axial positionof the ferrule which is in turn carried by its respective armaturemember.

Electrical or, in some embodiments, electric servomechanical circuitryis provided in cooperation with the structure of the above example toprovide the particular desired form of the electrical analog associatedwith the sensor. For example, each of the paramagnetic ferrulesmentioned may constitute an element in the magnetic clrcuit of a pair ofsensing coils associated with eac armature in a manner such that.movement of the arma-' ture causes opposite effects in the two sensingcoils associated with that armature. Then, due to the symmetry of thetwo armatures and venturis, the four sensing coils may be connected in adetecting bridge whereby displacement or motions of the armatures due toother than venturi effects are electrically cancelled out. Suchnon-venturi displacements may be due for example, to viscous drageifects of the fluid flow, acceleration of the meter environment,difierential thermal strains and the like. A corollary advantage of thistype of mechanical-electrical network is that the sensitivity of thesensing mechanism is vastly increased, over what it would otherwise be,due to the push-pull technique utilized in the network, Details of suchcomponents of the combination view of an alternative example of suchflowmeter structure (see lines 22 of FIG. 3 infra);

FIG. 3 is a cross-sectional view of the apparatus of FIG. 2 taken alongthe lines 33 thereof; 7

FIG. 4 is a schematic diagram illustrating a generalized example ofelectrical circuitry utilized in cooperation with the structure of theearlier figures;

FIG. 5 is a simplified diagram partially in longitudinal section andpartially schematic of an alternative embodiment of a flowmeter systemconstructed. in accordance with the principles of the present invention;

FIG. 6 is a schematic diagram of a more specific example of circuitrywhich is in some respects alternative to that illustrated in FIG. 4;

FIG. 7 is a longitudinal sectional view of a portion of an alternativeembodiment of the invention;

FIG. '8 is a schematic diagram of an example of the electrical circuitryutilized in combination withother flowmeter structure of the presentinvention;

FIG. 9 is a schematic diagram of circuitry similar to that of FIG. 8;

FIG. 10 isa simplified longitudinal sectional view of an alternativeembodiment of the flowmeter sensor structure of the present invention;

FIG. 11 is a' schematic view of an example of electrical circuitryutilized in combination with the apparatus illustrated in FIG. 10;

FIG. 12 is a partially sectional, partially schematic diagramillustrating an alternative embodiment of a flowmeter system constructedin accordance with the principles of. the present invention; and

FIG. 13, FIG. 14, FIG. 15, FIG. 16 and FIG. 17 are longitudinalsectional views of yet other examples of fiowmeter apparatus constructedin accordance with the teachings and discoveries of the presentinvention.

With specific reference now to the figures in more detail, it isstressed that the particulars shown are by way of example and forpurposes of illustrative discussion only and are presented in the causeof providing what is. believed to be the most useful and readilyunderstood description of the principles and structural concepts of theinvention. Inthis regard, no attempt is made to show structural detailsof the apparatus in more detail than is necessary for a fundamentalunderstandingjof'the invention, the description taken with the drawingsmakingapparent to those skilled in the art and technology of fiowmetershow the several forms of the invention maybe embodied in practice.Specifically, the detailed showing is not to be taken as a limitationupon the. scope of the invention which is defined by the appended claimsforming, along with the drawings, a part of'this specification.

Referring to FIG. 1, an example of a flowmeter 14 is illustrated whichincludes a central outer hollow cylindrical body portion 16' and a pairof enclosing end mem-- bers 1'8, 24 The end members are shown joined toxternal system piping 22 as by conventional threaded joining. The endmembers 18, 20 are axially compressively joined to the central bodyportion 16 by a series of tension supporting, peripherally distributed,axially oriented assembly bolts 2-4. The resulting confined volumewithin the body portion 16 and the end members 18, 20 forms what may betermed a series conduit body which communicates with the external.system piping 22 through axial ports 26, 28 provided respectivelythrough the end members 18, 20 in register with the threaded connectionsfor the external piping. Sealing O-rings 30, 32 housed withinappropriateretaining channels may be provided for hermetically sealing the assemblytogether while at the same time providing ready disassembly for accessto Sensing elements housed within the assembly.

The flowmeter sensing elements comprise a pair of venturi members 34,36-which are supported concentrically:

within the central body portion 16 coaxially therewithv and, with adegree of resilient axial motion, by annular diaphragms 38, 40, 42, 44.The former two are disposed one each at either end of the venturi member34 while the latter two are disposed supportingly at either end of theventuri member 36. The venturiv members are formed of a generally lowinertia structure which in this example is tubular aluminum with alarger inner diameter at each of their outer extremities, that is,contiguously to the end members 18; 20; and with a smaller innerdiameter near an axial central plane of symmetry from which. the venturimembers are each slightly axially spaced and about which they aredisposed in mirror image symmetryr Each ofthe venturi members carries aparamagnetic toroidal piston 46, 48 secured about the periphery of thecentral portion of each of the respective venturi members concentricallywith the axis of the system.

In operation, very briefly, fluid flow through the conduit system alongthe axis of the structure shown in FIG. 1, causes, by Bernouli eifect, adecreased pressure in the annular space 50, between the symmetric halvesof the unit, with respect to that existant in the annular chambers 52,54 at the ends of the. unit between the respecfive venturi members andthe end members 18, 20. This decreased pressure, the magnitude of whichis a measure of the rate of flow along the axis of the system permits,or causes, an axial displacement of each of the venturi members towardthe plane of symmetry at the center of the device. This axialmotioncauses a corresponding displacement of the paramagnetic pistons 46, 48which in turn afl'ects a magnetic-electric network in a manner to bedescribed in more detail below.

The remainder of the magnetic circuit housed within the body of thefiowmeter 14 includes, in this example,

four paramagnetic cup members 56, 58, 60, 62.'Each of the cup membersincludes an outer rim portion 64 and an annulus portion 66 which iscentrally ported to provide clearance for the venturi members. and whichis joined at itsv outer periphery to one end of the rim portion 64. Thecup members are arranged in. pairs symmetrically about each of theparamagnetic pistons, 46, 48 with concave configurations beingjuxtaposed toward each other. Disposed symmetrically within each of thejuxtaposed pair of cup members is a symmetrically ar-- rangedsecond pairof paramagnetic members 67, 68, 70,

72 which each comprise an annulus portion 74 joined with an inner rimportion 76. The pair of the paramagnetic members 67, 68, 70,. 72. arearranged with theirannulus portions juxatposedand in contact at theirouter peripher ies with a respective one of the paramagnetic cup members56, 58, 60, 62 and with their inner rim portions 76 projecting axiallytoward a respective one of the annulus portions 66 of'the cup members.The end of the inner rim portion 76 does not contact the annulus portion.66 of the cup members but is axially spaced therefrom; to

form a high reluctance gap in the otherwise permeable loop around thetoroidal cross-section formed by the cup members and the paramagneticmembers 67, 68, 70, 72. The inner cylindrical surface of the rimportions 76 is each radially juxtaposed with respect to the outercylindrical surface of a portion of a respective one of the paramagneticpistons 46, 48. As may then be seen from the figure, axial motion of theventuri members increases or decreases the axial length of the effectivehigh-reluctance gap in the magnetic loops formed by the cup members, theparamagnetic members 67, 68, 70, 72, and the paramagnetic pistons 46,48.

A toroidal spool 78 wound with a sensing coil 80 is interposed withineach of the magnetic toroids just described. These coils areadditionally labeled A, B, C and D for ready correlation with certain ofthe subsequent circuit diagrams.

In the assembly of the end members 18, 20, the central body portion 16,and the paramagnetic sensing elements and diaphragm members within thebody portion, a series of spacing rings are disposed in a. stackingmanner with the other elements in a manner to determine and secure thedesired axial relationships therebetween. It may be noted that thespacing rings are all relatively radially thin except for thosecompressively juxtaposed between the annulus portions 74 of theparamagnetic members 67, 68, 70, 72. These latter spacing rings may havea radial dimension substantially equal to that of the annulus portion ofportions 64.

Referring to FIG. 2, an alternative example of the invention isillustrated which includes a pair of magnetic venturi members 86, 88which, in addition to being fabricated integrally with the paramagneticarmature por tion 90, 92, are formed, or disposed with their largerdiameter portions placed axially adjacent to each other with the smallerdiameter portions being disposed near the end members 18, 20. Theremainder of the magnetic circuits for the sensing elements compriseparamagnetic collar members 94, 96, 98, 100 which are toroidal with atorus cross section having a cup shape which is open in one axialdirection. The paramagnetic collar members are disposed in pairs withtheir concave or open torus portions being juxtaposed toward each otherwith a respective one of the paramagnetic armature portions 90, 92interposed therebetween. The toroidal magnetic loop circuit is then seento be formed by the cup shaped torus section of the collar members incooperation with the radially extending paramagnetic armature portion90, 92. Each of the collar members 94, 96, 98, 100 may also be describedin this example as being formed by a pair of radially spaced rim members102, 104 interconnected by an annular plate 106. Within the torus cupformed between the rim members 102, 104 is disposed the sensing coils 80(A, B, C, D) wound in the spools 78. Shown also in the view of FIG. 2are the electrical leads to thelsensing coils which extend from theindividual sensing coils as shown to a hermetic connector plug 108.

Referring to FIG. 3, the central sectional view therein presented showsthe hermetic connector plug 108 in elevation as mounted to the centralportion of the body member 16. The peripheral distribution of theassembly bolts 24 is shown more clearly in this view as is the centralone of the spacing rings 82 and one of the annular diaphragms 40.Concentric annular corrugations 110 in the diaphragm member may also beseen in the view of FIG. 3. The large diameter end of the venturi member86 is also illustrated in this view.

In FIG. 4 a schematic diagram of an example of a flowmeter sensingcircuit is illustrated in which the four sensing coils 80 (coil A, coilB, coil C and coil D)'are connected in a bridge circuit with the coilsconnected in a loop ABCDA, clockwise as shown in the figure, with analternating current generator connected between the opposite points atthe junction between coils A and B and the junction between the coils Cand D, and with 6 a meter M connected between the other opposite looppoints; that is, between coils A andB and between coils B and C.

In operation it may be seen that initially the bridge may be balanced ifthe inductive reactance of each of the coils is equal. In this event,there would be no current through the meter M. It may also be seen thatwhen the venturis are moved in the same direction as by vibration oracceleration effects, the changes in inductive reactance cancel and thebridge remains balanced. When, however, the fluid is forced through theventuri members, they are displaced axially away from each other causingthe inductive reactance of coils B and C to be lowered while that ofcoils A and D is increased. Thusly, the bridge network is unbalanced ina push-pull fashion so that current from the alternating currentgenerator flows predominantly through coils B and C, effectively inseries with the meter M, while less current flows through the coils Aand D. The magnitude of unbalance of the bridge network and consequentlythe level of current through the meter M is clearly a measure of themagnitude of fluid flow through the flowmeter 14.

It may be noted that, typically, the specific object when measuringfluid flow is to obtain the mass rate of flow (M), i.e., mass per unitof time of the gas or liquid past a given point. For incompressiblefluids, the density (mass per unit of volume) may be assumed to beconstant, ignoring second order temperature and pressure eifects.

In the examples of the invention thus far described, the electricaloutput of the flowmeter is generally proportional to the mass rate offlow times the fluid velocity (Mv). Thus, the mass rate of flow may beobtained by dividing, electrically this quantity by the velocity v. Thismay be accomplished by the structure illustrated in FIG. 12 below.However, the mass rate of flow may also be obtained by taking the squareroot of the quantity Mv, since from the continuity equation (M= gvA,where pg is the fluid density, and A is the cross sectional area of thefluid conduit at the point of observation) P9 and by substitution 2 2M1) (the meter output) g KM where k is a constant for an incompressiblefluid. A standard, shelf unit is then used to operate electrically onthe flowmeter output to obtain the quantity M.

For compressible fluids, wherein the density varies as a function oftemperature and pressure which must be accounted for, consider againthat the electrical output of the flowmeter is m M y Pg RT where NR isthe appropriate gas constant and T is the gas temperature. In thisequation, g may be determined from the gas equation i NRT where P is thegas pressure. An electrical analog of P may be obtained from a pressuresensor and of T from a temperature transducer. Thus by dividing themeter output by gNRT, the quantity M is obtained, the square root ofwhich is the desired quantity.

Referring to FIG. 5 an example of the invention is illustratedschematically in which the degree of unbalance in the bridgenetwork isutilized to drive a servo in order, automatically, to null the currentthrough the meter M. This is accomplished in an embodiment'where fluidflow causes the venturi members to separate, as in the example of FIG. 2and an electrical solenoid is used to drive the venturi members back totheir balanced disposition. The solenoid type force required so to drivethe venturi members is substantially proportional. to the square of themagnitude of the solenoid current. Thusly, since the resultant axialforces due to the Bernouli efiect are substantially proportional to thesquare Ofthe velocity of fluid flow, the driving current for thesolenoid servo is directly proportional to the velocity of. the fluidflow through the venturis, for non-compressible fluids.

When this example of. the invention is utilized-t obtain M for acompressible fluid, the output. of the flowmeter,

may be operated upon as follows:

Z NRT may be obtained, as discussed above, from pressure andtemperaturepickups and performing electrically the indicated arithmetic. Then byextracting the square root of g thus obtained, the result may be dividedinto the fiowm'eter output to obtain M.

It may also b'enoted that the present invention may be utilized toobtain the quantity g'for gases. From the continuity equation, it' isclear when M and v areknown (v being; obtained as by the embodiment ofFIG. 12' below), pg is readily obtained straight forward electricalarithmetic operation.

Similarly, a gas constant meter is readily provided in accordanceWithandther arrangement of the presentinvention: from I P NRT' or P NR=p it is apparent that by appropriate operation upon the output of thedensity g)meter above,a pressure sensor, and a temperature sensor, thequantity NR may be provided dynamically and directly.

The apparatus of FIG. includes a pair of cylindrical E coils 114, 116which are each wound with a sens ing coil 118. Thev axialy resilientlydisplaceable venturi members 120' each carry a" paramagnetic ferrule 122which forms a portion of the variable reluctance magnetic' circuit foreach of the halves of the cylindrical E coils. In addition to' each ofthe paramagnetic ferrules 122, each of the venturis 120 carries aparamagnetic end portion 124, 126 which together cooperatively form: aportion of the solenoideii'ect magnetic servocoil 128; Asindicatedearlier, the coils 118" are connected in a bridge network which isexcited by an alternating" current generator, and the output of which isfed to an amplifier 132 which in turn drives the magnetic servo coil 128to maintain the balanced state or disposition of the venturi armatureswithin'the" flow-meter apparatus; The current'required" to maintain thisbalance is indicated" or recorded by the instrument 130.

Referring to FIG. 6, an'alternative example of a detecting circuit whichhere incorporates a demodulator for the sensor or transducer system isillustrated. Inithisexample the current feed from the alternatingcurrent generator is impressed upon the movablecenter tap of'each of a.pair of potentiometers 136, 138,.the fixed resistance of. which isinterconnected respectively between. coils Avand Cand between coils Band'D. The opposite terminals offcoils A and D are interconnected by adiode rectifier bridge 140 while the corresponding terminals of coilsBand. C are interconnected by a similar detectingbridge 142. Theoutput-terminal. pair of the detector bridges 140and 142-are connectedtogether in parallel with an indicator or recording instrument 144-connected therebetween. The bridge output as seen, at the instrument 144is of course a direct current voltage; and theoverallibridge,includingthe major legscomprisingthe:coils.A,.B, C and D,operatesbasically' in the same manner as does the similar bridge of FIG.4. In the example of. the network of FIG. 6 however, either one of. thepotentiometers 136, 138- may be utilized to balance or null the bridgeunder static conditions. Both otentiometers may then be shifted to theleft or right in. parallel. to. control the sensitivity of each armatureand its correspondingv magnetic. circuit thus. making their sensitivitythe: same even t-houghduring their manufacture there may havebeenslightdifierences in the weights of the armatures. or different springconstants for the supporting diaphragms due to manufacturingimperfections anddiiferences in materials. In this manner then, thenatural frequency of each. diaphragm-armature system canv be'completel yelectrically compensated andbalanced with the other thereby insuring abalance of the instrument.

ffom both a mechanical (sensitivity) and an electrical viewpoint.

Referring to FIG. 7, an example of the invention is illustrated whichutilizes a single axially resiliently displaceable armature member whichis supported as in the previous examples by an annular, axially flexiblediaphragm 152. The diaphragm 152 may be fabricated of paramagnetic metalor. is made effectively paramagnetic, as shown, by. the bonding theretoof an annular paramagnetic ring. member 156 The ring member may bemounted concentrically on the left hand face, as viewed in the drawingof the diaphragm. 152 and is axially spaced from and juxtaposed withrespect to a toroidal cup member 166-. The toroidal cup is formed by anouter rim member 162, an inner rim member 164,. and an annular diskmember 166 interjoining their left hand peripheries as shown. The cupmember thusly formed and the annular disk or ring member 156 form incooperation, a magnetic circuit about the periphery of'the rectangulartoroid generator form; the magnetic circuit including a pair of gapsI68; 170.

The toroidal cup member 160 is in this example supported rigidly withrespect to the outer body member 172 by a rigid. nonmagnetic annulardisk member 174. A second, inner disk member 176 is supportinglydisposed between the inner paramagnetic rim member 164 and a stationaryinput conduit member 178'. The right hand end of the conduit member 178is partially occluded by an end member 180 having a right hand end face182 Which, in the absence of' fluid flow through the system, is-disposedin juxtaposed contact with the left hand face 184 of the-armature member150. In this example the end member 180' of the stationary inlet conduitmember 178 is centrally ported by an axial duct 188 and a. plurality ofbleeder capillaries I90; The axial duct 188communicates with theinterface boundary between the faces 182, 184 While the bleedercapillaries 19 0 communicate with. the toroidal space 192' between thejuxtaposed diaphragm 152 and'the annular disk members 174, 176. Thearmature member. 150' is ported to form a plurality of: axial ducts'194'which' also communicate with the interface boundary between thefaces 182, 184.

Under conditions of zerofl'ow, the ends of the axial ducts 188, 194 atthe interface boundary are substantially sealed from each other byvirtue of the diaphragm 152, which retains the armature member 150 incontact with the end" face 182'. This axial disposition of the armaturemember 150' causes a predetermined minimum axial gap dimension to existfor the gaps 1'68, 170 for the magnetic circuit of a solenoid sensingcoil H6 wound and disposed in a spool fashion within the toroidal cup ofthe member 160. When, however, a minute flow in the direction of'thearrow 198 tends to flow in the direction indicated, a pressure isimpressed upon the left hand face of the supporting, diaphragm 152,.through thecapillaries and uponthe-central portion of the left hand face184 of the armature;- member 150 resulting in an axial force to theright of. the armature member and its supporting diaphragm. 152. Such anaxial displacement results in a definite change in the reluctance of themagnetic circuit formed by the paramagnetic toroidal cup member 160 andthe ring member 156 carried by the supporting diaphragm 152. Theresulting sensor assembly or transducer system is thus extremelysensitive to near zero flow rates and provides a precision measuringfunction in flow metering not heretofore available.

Referring to FIG. 8, an example of the invention is illustrated whichmay be mechanically substantially identical to that of FIG. 1 but whichis electrically a variation thereof in that the sensing coils A, B, C,D' are bifilar or double wound so that each includes an insulated pairof mutually inductively coupled coils. For example, the sensing coil Acomprises a pair of windings 200, 202; the coil B comprises a pair ofwindings 204, 206; the sensing coil C includes windings 208, 210; andsensing coil D' includes a pair of windings 212, 21-4. The paramagneticpistons 46, 48 (see FIG. 1) are seen from the schematic view of FIG. 8to affect, by their axial position, the magnitude of mutual inductanceand thereby the coupling, between the associated pairs of windings ofthe sensing coils. The direction of the motion arrows 216 for example,indicates, again with reference to FIG. 1, that an increase in thevelocity of fluid flow through the flowmeter causes a decrease in thecoupling between the bifilar windings of the sensing coils A and D witha corresponding increase in the coupling between the windings of thesensing coils B and C.

In this example of the invention, the coil windings 200, 204, 2.08, 212are all connected in series with a source of alternating currentexcitation signal and comprise the composite primary winding of what maybe termed a sensor transformer. The secondary windings 202, 206, 210,214 of the transformer are coupled to a nulling transformer 220 whichhas a pair of primary windings 222, 224 connected as follows: thewindings 206, 210 are connected in series with each other and with theprimary winding 222 of the nulling transformer 220; and the windings202, 214 are similarly connected in series with each other and with theprimary winding 224. These connections are polarized in a manner suchthat under static conditions of zero flow through the flowmeter, thesignals from the generator coupled to the secondary windings ofthesensing transformer, which are in turn coupled to the primary windings222, 224 of the nulling transformer, are exactly opposed and cancelwithout coupling any signal to the secondary winding 226 of the nullingtrasformer. When, however, motion, in accordance with the arrows 216,occurs of the paramagnetic pistons 46, 48, the coupling to the secondarywindings 206, 210 and thence to the primary winding 222 is significantlyincreased while the coupling to the windings 202, 214 and thence to theprimary winding 224 is significantly decreased. The net resultant signalin the primary of the nulling transformer 220 is then coupled to thesecondary winding 226 which may be full wave rectified by a bridgenetwork 230 the output of which is observed or recorded at the meterinstrument 232.

Thusly, in a push-pull mode of operation, the magnitude of the flow ratethrough the meter system is manifest directly and substantiallyinstantly on the meter instrument 232. It should be noted that althoughthe electrical network of FIG. 8 has been referenced specifically to thestructure shown previously in FIG. 1, the network as shown and itsprinciples of operation apply with equal validity to various others ofthe structural embodiments of the invention.

In FIG. 9, an alternative electrical circuit for the basic structure ofFIG. 8 is illustrated. In this example, the excitation coil windings200, 206 are connected in series as are the windings 208, 212. The tworesultant series are then connected in parallel across the excitationgenerator. Interposed in each of the series is a potentiometer 213, 215respectively. The potentiometers provide a control on the sensitivity ofeach of the armatures.

The sensing windings'202, 214 are connected in series with each otherand with a detecting bridge circuit 217. The other two sensing windings2.04, 210 are similarly connected in series with a detecting bridgecircuit 219. Each of the sensing series may also include a potentiometer221, 223 respectively for balancing, or nulling, the output signal whichis provided, as indicated, between the symmetrically interconnecteddemodulator bridge circuits 217, 219. A recording or indicatinginstrument M may be connected, as shown, between the two bridges. Theoperation of the excitation-sensing variable coupling apparatusincluding the venturi armatures and the 'bifilar coil windings, issubstantially similar to that of FIG. 8.

In FIG. 10, in highly simplified form, an example of the invention isillustrated which is similar in most respects to the previous examplesexcept that the sensing mechanism is base-d upon the variation of acapacitance parameter rather than one of inductance. To this end, a pairof venturi armature members 240, 242 are shown which each, insymmetrical fashion, carry an annular capacitor plate member 244, 246respectively. The venturi armature members may be supported as in theprevious examples by appropriate axially flexible metallic diaphragms,not shown. Axially juxtaposed with respect to each of the faces of thecapacitor plates 244, 246, are mounted stationary annular disk capacitorplates 248, 250, 252, 254. It may thus be seen that the juxtaposed facesand the gap between them of the plates 248, 244 constitute a capacitordenoted C Similarly, capacitor C is formed by juxtaposed faces of theplates 244, 250, a capacitor C by the juxtaposed faces of the plates252, 246, and a capacitor C by the juxtaposed faces of the plates 246,254.

The four resulting capacitors may then be coupled in a bridge networksuch as that illustrated in FIG. 11. Flow through the otherwise balancedflowmeter sensor causes a displacement of the venturi armature members240, 242 toward each other as indicated by the motion arrows 256. Thisdisplacement results in a decrease of the capacitive reactance of thecapacitors C and C which unbalances the bridge 2,58 and results in a netalternating current signal flowing through the meter instrument 260, dueto the increase in magnitude of current through the capacitors C and Cwith respect to that through the capacitors C and C Referring to FIG.12, an example of the invention is illustrated which utilizes a venturiflow sensor transducer system 264 similar, for example, to that shown inFIG. 1, and a bridge network 266 similar to that illustrated in FIG. 4.This system provides what is termed a true mass system 264 simliar, forexample, to that shown in FIG. 1 meter by which is denoted a transducersystem which provides an electrical signal output which is proportionalto the mass flow per unit time through the conduit of the system forsubstantially all fluids including compressible fluids. To this end apropeller device 268 is mounted on a strut apparatus 270. At least oneof the blades of the propeller device is fabricated of magnetic materialor includes a magnet or magnetic material insert in one or more of theblades. A magnetic or variable reluctance pick-up transducer 272 ismounted on the external wall of the conduit of the system in magneticinteraction relationship with the magnetic material in the propeller ofthe device 268. The frequency of the signal output of the transducer 272is, for all fluids including compressible fluid, substantially directlyproportional to the velocity of the fluid through the conduit of thesystem. The signal is impressed through the leads 274 to one input of adividing network 276 while the output signal from the bridge network266, which is proportional to the mass flow times the velocity, isimpressed through the leads 278 onto a second input terminal of thedividing network 276. The network 276 may be a conventional dividingnetwork which divides the bridge network output signal by the pick-uptransducer 272 signal output and obtains at its output terminals 280, asignal which 'is directly proportional to H the true mass rate of flowthrough the conduit of the system. a

In FIG. 13, a single diaphragm embodiment of the inventionis illustratedwhich includes a housing body 282 which may be constructed and assembledsubstantially similar in all important respects to that of the exampleof FIG. 1. In this example, however, multifilar toroidal coils 284, 286each wound on a phenolicbobbin 288 are each disposed within awtoroidalmagnetic circuit comprising an outer rim member 290, an inner, magneticstainles rim member 292 and an annular interconnecting disk member 294.Each of theserirn and disk members are fabricated of low reluctanceparamagnetic material. The outer rim members 290 are circumferentiallysandwiched about the periphery of a permeable diaphragm member 296 whilethe inner rim members 292 are each axially spaced slightly therefrom.Thus, it may be seen that the magnetic circuit for each of the coilsincludes the axial length of an outer rim member 290, the radial widthof an annular connecting disk member 294, the axial length of an innerrim member 292, the gap between the permeable diaphragm member 296 and ajuxtaposed end of one of the inner rimmembers-292, and the radialdimension therefrom, through the permeable diaphragm to the outer rimmember 290.

Under static conditions, the reluctance of the two circuits may be madeequal or electrically balanced externally.

The diaphragm member 296 is centrally apertured as shown to form an opennozzle portion 300, which has a larger diameter at its left hand endwhere it joins the radially planar outer portion of the diaphragmrnemberthan it has at its right hand end which forms the outlet of the nozzle.The nozzle effect when fluid is passed through. the device in thedirection of the arrows 298, provides, as does the Bernouli effect inthe above examples, a reduced pressure to the right of the nozzleportion 300 such that the magnitude ofthe pressure differential oneither side of the permeable diaphragm member 296'is proportional to thesquare of the velocity of the fluid flow therethrough. The resultingforce to the right on the diaphragm member causes an axial displacementthereof which decreases the reluctance of the magnetic circuitassociated with the coil 286- and increases the reluctance of themagnetic circuit associated with the coil 284. This difference ininductive reactance or in mutual inductance between individual ones ofthe windings of the rnultifilar coils'may :be utilized, as in theprevious bridge networks shown, to provide an observable or recordablemeasure of the velocity of the flow of fluid through the device.

, Referring to FIG. 14, an example of the invention is illustrated inwhich the sensing means for detecting the axial displacement of a pairof venturi armature members 300, 302' includes a strain gage networkmechanization. In the example shown, each of the armature venturimembers carries an inner end 304 of a plurality of angularly equallydistributed strain gage supporting spring members 306, the radiallyouter end 308 of each of the spring members is atlixed to a stationaryposition on the inner wall of the housing body 310 by aseries offerrule-like spacers 312 as shown. In this example of the invention,four of the supporting spring'members 306 are utilized angularlysymmetrically spaced about each of the armature venturi members. Notethat in the figure only two of each set are shown. Each of the springmembers carries an elongated strain gage wire supporting insulated rod3'14, whichmay' have a quartz; sapphire, or the like, composition, suchthat flexing of the spring member 306 due to axial displacement of thearmature venturi members causes a rotation of the sapphire supportingrod about its center and in an axial plane. This rotation of the rods issymmetrical causing those rod ends 316 closest to the plane of symmetryof the sensor device all to move radially outwardly, for example, whenthe fluid flow rate through the device is increased as indicated by thearrows.

318 while the outer ends' of the sapphire rods are caused to moveradially inwardly as indicated by the arrows 320. Each end of theinsulated rods is circumferentially grooved as shown to form a set ofretaining channelsfor a multi-turn circumferential strain gage sensor322.

The four sensors in this example each comprise two com plete turns ofstrain gage sensor wireand are labeled, for

analogous correlation with the circuit diagrams discussed earlier, A, B,C", D rom left to right in the figure, The resulting set of strain gagesensor elements may then. be connected in a push-pull or bridge networksimilar to any of those shown or discussed earlier hereinabove and theresulting operation is substantially identical thereshown in the earlierfigures is connected to a plurality of strain gage wire sensing elements330 which are connected in tension between an axially central locationon the outer housing body 332 and an axially outer point ona respective:one of a pair of venturi armature members 334, 336. Similarly, asetofstrain gage wire sensing elements 3138 are connected-in a tensionsupporting relation between an axially outer position on the housingbody 332 and an axially inner point on a respectiveone of the venturiarmature members 334, 336. Each set-of the wire sensing elements 330,338- may be arranged in angula-rly symmetric distribution throughout thetoroidal space between respective ones of the armature members and theouter housing body; and each set may be connected in series asindicated, for example, by the leads 640, 342, 344, 346. Then each ofthe four sets maybe connected into a bridge network as. in the case of.the apparatus discussed and described in connection with FIG. 13.

, Referring to FIG. 16 the structure illustrated may be identicalwiththat of FIG. 15 except that instead of utilizing strain gage-wiresas the strain sensing element, different sets of miniature strain gageelements 348- maybe bonded in an appropriate array to the axiallyresilient armature supporting diaphragms as shown. Again, the differentsets of strain gages may be appropriately connected in series to providethe desired sensitivity and to form the desired number of sets thereoffor interconnection intothe desired bridge or other detectingnetwork.

Referring to FIG. 17, an example of the invention is illustrated whichis particularly useful invibratory, or otherwise accelerating,environments. In the figure only one half of the 'flowmeter transduceris illustrated, it be ing understood that the apparatus shown in detailmay be axially, symmetrically repeated from a plane ofsymmetry disposedat either end of the portion illustrated.

In this example, the flowmeter 350 comprisesan outer cylindrical housingbody 352 within which is disposed a'series of annular spacers 354 forremovably securing-the axial displacement of the internal componentparts of the transducer. Anaxially movable venturi member 356 issuspended between a pair of annular, supporting diaphragms 358, 360.Suspended axially within the diaphragms 358, 360 is a movable coilassembly 362which is similarly supported by a pair of annular diaphragms364, 366. The coil assembly 362 comprises a pair of symmetrical,juxtaposed, annular, magnetic, coil supports- 368, 370 which are spacedfrom their plane of symmetryby a magnetic member 372 which includes anannular. disk portion 374 and aninner rim portion 376 extendingsymmetrically toward radially inwardly extending portions of each of theannular coil supports 368, 370. Interposed between the juxtaposedportions of. the inner rim portion 376 and the inwardly extendingportions of the supports 368, 370, respectively, isa radially outwardlyextending v 13 flange portion 378, 380 of a magnetic armature member382, the latter being aflixed to the movable venturi member 356. Theradial gap 384 between the cylindrically juxtaposed central portions ofthe armature 382 is as small as possible whereby, having a large area ofjuxtaposition, its reluctance is relatively small compared to the axialgaps between the ends of the rim portion 376 and the coil supports 368,370. These latter are not totally filled by the flange portions 378, 380and, accordingly, these axial gaps are variable depending upon therelative position of the armature 382 carried by the venturi member 356.

Each of the coil supports 368, 370 has associated therewith a sensingcoil 386, 388, respectively. Each is wound on a bobbin 390, 392 andemplaced within the toroidal volume defined by the magnetic coilsupports 368, 370 and the magnetic member 372.

The operation of the transducer as varying the reluctance of themagnetic circuit of each coil and, thereby, its-inductive reactance issubstantially as discussed earlier in connection with the previousfigures. The primary distinction of the present embodiment is that thesensing coil assembly is also suspended on axially flexible diaphragms.In the practice of the invention, the natural frequencies of the twosuspended bodies (venturi assembly and coil assembly) are made equal asdetermined by their masses and eflective spring constants. For purposesof providing a fine frequency adjustment for equalizing the two naturalfrequencies associated with half of the fiowmeter, a balancing coil 394is disposed contiguously about and in a solenoid eifect relationshipwith the coil assembly 362. Thus, by varying the current through thecentering coil 394, the effective spring constant of the movable coilassembly 362 may be controlled. By this means, the in strument is madeelectrically insensitive to vibration or other accelerations, becausethe acceleration induced movements of one part of the transducer areduplicated by the other so that the relative displacement between them,as affecting the magnetic circuits of the sensing coils, is zero.

Another class of examples ofthe invention, not specifically depicted,comprises a cylindrical housing body 16 such as illustrated in FIG. 1,for example, but which instead of beingcoupled to system piping 22, issuspended on rigid struts within a fluid conveyor of relatively muchlarger diameter than that of the housing body portion 16 of thefiowmeter 14. The fluid then flows over the external surfaces of thefiowmeter as well as through the axial apertures in the end members 18,22. The meter operates exactly as in other embodiments discussed aboveexcept that a straight forward correction is made in the electric ormechanical apparatus for the proportionally, and somewhat smaller,velocity through the fiowmeter as compared with the velocity of flowaround the meter.

There has thus been disclosed and described a number of examples of anelectromagnetic fiowmeter system and method according to the presentinvention which exhibit the advantages and achieve the objects set forthhereinabove.

What is claimed is:

1. A fiowmeter structure for measuring fluid flow therethrough,comprising:

first and second venturi members, defining flow channels varying from alarge sectional dimension to a smaller sectional dimension, to provideinternal tapers;

diaphragm means for flexibly supporting said first and second venturimembers independently and spaced apart, to receive said fluid flowwhereas solely said fluid flow through said venturi members displacessaid venturi members, said first and second venturi members beingsupported by said diaphragm means to position the internal taper of saidfirst venturi member in opposing relationship to the internal taper ofsaid second venturi member; and

means for sensing displacement of said first and second venturi membersresulting from fluid flow there- 14 through whereby to manifest ameasurement of said fluid flow.

2. A fiowmeter structure according to claim 1 wherein said first andsecond venturi members are supported by said diaphragm means to beoppositely displaced to a degree related to said fluid flow therethroughand wherein said means for sensing manifests such opposed displacement.

3. A fiowmeter structure according to claim 2 wherein said sensing meanscomprises electromagnetic means for sensing displacement as anelectrical signal.

4. A fiowmeter structure according to claim 2 wherein said venturimembers are similarly symmetrical.

5. A fiowmeter structure according to claim 1 wherein said first andsecond venturi members define similar flow channels and wherein saiddiaphragm means support said venturi means in aligned spaced-apartrelationship to provide similar facing apertures.

6. Flowmeter structure comprising:

conduit body defining an axial path therethrough for fluid substance;

a pair of venturi members each having two end portions and beingdisposed substantially axially symmetrically to each other on oppositesides of a plane of symmetry disposed transversely across said path;

' centrally apertured axially flexible diaphragm members aflixedsupportingly to said venturi member at each of their four said endportions; and

axial displacement strain sensitive electric sensing elements coupled toat least some of said diaphragm members for detecting axial displacementof said venturi members with respect to said conduit body.

7. Meter apparatus comprising:

substantially rigid conduit body defining a flow path for fluidsubstance axially therethrough;

first pair of axially flexible diaphragm members disposed within saidconduit body contiguously to a plane of symmetry extending transverselyto said flow path, said diaphragm members being centrally apertured topermit the flow of said fluid substance;

second pair of axially flexible diaphragm members similarly aperturedand disposed one each substantially symmetrically from said plane ofsymmetry and separated axially from an associated one of said first pairby a predetermined axial length; and

a pair of venturi members each comprising a hollow cylindrical-like formhaving a length substantially equal to said predetermined axial lengthand having a tapered inner diameter which varies smoothly from a minimumdiameter toward one end to a maximum diameter toward the other,individual ones of said venturi members being supported in axiallymovable relation, with respect to said conduit body, by the radiallyinner portions of a predetermined one of said pairs of said diaphragmmembers on either side of said plane of symmetry, said two venturimembers being disposed with their tapered inner portions axiallysymmetrically imaged from said plane of symmetry.

8. Flowmeter apparatus comprising:

substantially rigid conduit body defining a flow path for fluidsubstance axially therethrough;

first pair of axially flexible diaphragm members disposed within saidconduit body contiguous to a plane of symmetry extending transversely tosaid flow path, said diaphragm members being centrally apertured topermit the flow of said fluid substance;

second pair of axially flexible diaphragm members similarly aperturedand disposed one each substantially symmetrically from said plane ofsymmetry and separated axially from an associated one of said first pairby a predetermined axial length;

a pair of venturi members each comprising a hollow cylindrical-like formhaving a length substantially equal to said predetermined axial lengthand having a tapered inner diameter which varies smoothly from a minimumdiameter toward one end to a maximum diameter toward the other,individual ones of said venturi members being supported in axiallymovable relation, with respect to said conduit body, by the radiallyinner portions of a predetermined one of said pairs of said diaphragmmembers on either side of said plane of symmetry, said two venturimembers being disposed with their tapered inner portions symmetricallyimaged from said plane of symmetry; and axial displacement sensitiveelectric sensonmeans coupled between said conduit .body and at least oneof said venturi members. 9. The invention according to claim 7 in whichfirst pair of diaphragm members are axially separated by a distanceshort compared to the transverse dimensions of 'said diaphragm memberand in which the inner portions .ofseach of said'centrally apertureddiaphragm members are peripherally sealed to said end portions therebyto form an annular space about said plane of symmetry which communicateswith said axial fluid flow path.

10. The invention according to claim 8 in which said electric sensormeans includes a paramagnetic element .carried by at least one of saidventuri members and magnetic circuit means carried by said conduit bodyand magnetically coupled to said paramagnetic element to a predetermineddegree the magnitude of which is dependent .carried respectively byseparateones of saidventuri mem- -bers,.said first paramagnetic elementbeing magnetically intercoupled in the reluctance circuit between thebifilar 'windings of said first coil and in the reluctance circuitbetween the bifilar windings in said second coil, said sec- .ondparamagnetic elementbeing similarly magnetically intercoupled. in thereluctance circuits respectively of said third andfourth bifilar coils;and the invention further including an alternating excitation meanscoupled to one winding ofeach'ofsaid four bifilarcoils, the otherwinding of eachcoil constituting signal pickup windings.

13. Theinvention according to claim '8 which further includesservo-mechanical meanscoupled to said venturi members for .afiectingtheir relative axialdisplacement.

14. Meter system comprising-: conduit body member-defininga flow pathfor fluid substance axially therethrough;

first pair of axially flexible diaphragm members dis posed within saidconduit body member contiguously to a plane'of symmetry extendingtransversely to .said flow path,'said diaphragm members being centrally,ap'ertured'to'permit the flow of said fluid substance therethrough; i

second pair of axially flexible diaphragm -members similarly aperturedand disposed one each substantiallysymmetrically from said plane ofsymmetry, and separated axially from an associated one of said .firstpair by a predetermined axial length;

a pair of venturi members each comprising a hollow cylindrical-like formhaving a 'length'substa-ntialiy equal to said predetermined axiallength, and having a tapered inner. diameter which varies smoothly froma minimum diameter toward one end to a maximum diameter toward the otherend, individual ones of said venturi members being supported in anaxially restoringrelation with respect to said conduit body, by theradially innerportions of apair of said diaphragm members on either sideof said plane of symmetry, said two venturi members being disposed withtheir tapered inner portions substantially symmetrically imaged fromsaid plane of symmetry; axial displacement sensitive,.electric sensormeans coupled between said conduit body member and at least one of saidventuri members, said electric sensor means including first,second,.third and fourth coils constituting bridge elements ofavdetector network and carried'by said conduit body; first paramagneticelement carried by one of said venturi members and being magneticallyintercoupled conjugatively the reluctance paths of said first and secondcoils; and second paramagnetic element carriediby the other of saidventuri members andmagnetically intercoupled conjugativelyin thereluctancepaths of said-third and fourth coils.

References Cited UNITED "STATES PATENTS RICHARD C. QUEISSER, PrimaryExaminer.

EDWARD D. GILHOOLY, Assistant Examiner.

